(1) Field of the Invention
The present invention relates to a magneto-optical disk recording device, and more particularly to a magneto-optical disk recording device with means for verifying a recorded state during the recording and checking an erased state during the erasing in the magneto-optical disk.
(2) Description of the Related Art
In an optical disk medium, especially in a magneto-optical disk recording device which uses a magneto-optical disk medium typically represented by an erasable optical disk medium, a laser beam is converged and irradiated along a groove (guide groove) provided in advance on a magneto-optical disk medium formed of a thin magnetic film, thus magnetically recording data as magnetic patterns on the magneto-optical disk medium.
The groove is provided in a spiral form and, in the case of the magneto-optical disk medium, the groove is utilized for positioning a magnetic head to an adjacently located land region serving as a data track. In the data track, a sector format region for sector data is written in advance as a sector head region. In the magneto-optical disk recording device, the recording/reproduction of data starts upon the recognition of the pre-format. Conventionally, there are various methods for recording and reproducing data in the data regions that are divided into sectors. For example, in a 5-inch magneto-optical disk recording device, a mark position recording system is used for the recording. In this system, the recording is made by making the center of the recording pit hold data in accordance with binary data. In the re-recognition of the data to be reproduced, the read signal is differentiated and the zero cross point is detected. At the same time, the reproduction clock determined by the modulation system is extracted, and the pattern of "0" or "1" is judged from the timing relationship with respect to data detection windows, thus carrying out the reproduction of the original data.
Further, for the magneto-optical disk recording device for carrying out recording and reproduction of a large volume of data, there is research and development on a mark-edge recording system in which edges of the recording pit are made to hold data for the purpose of increasing the recording capacity. As for this system, it is known that the recording density can ideally be doubled as compared with the mark position recording system. During the reproduction, the edge data is detected normally by a fixed slice leveled pulsation and, simultaneously with this, the reproduction clock determined by the modulation system is extracted, and the pattern of "0" or "1" is judged from the timing relationship with respect to data detection windows, thus carrying out the reproduction of the original data.
With respect to the present-day magneto-optical disk recording device, for the reasons that the device lacks an overwrite function unlike in the magnetic recording device and that the device is easily contaminated with dirt or such damages as scratches, it is the practice to make the verification during the data recording in order to ensure the reliability of the recorded data. However, the read waveforms during the recording are different from the read waveforms during the normal reproduction so that, according to the conventional reproduction signal detection method, it has not been possible to detect the reproduction signal during the recording. Thus, the current process requires three steps, namely, data erasing, data recording and recorded data verification (the time period corresponding to three rotations of the disk) resulting in the problem that high speed recording is not possible. Recently, a magneto-optical disk medium having an overwrite function has been developed, and hence the standardization of the next generation optical disk medium is under consideration. However, in this case, only costly devices or systems have been proposed wherein, for example, the optical head has two-beam configuration or two optical head configuration for the verification.
A prior art magneto-optical disk recording device having a verification function is shown by a block diagram in FIG. 1.
The prior art device shown in FIG. 1 employs a two-beam optical head 1' with a reproduction beam 20 and a recording beam 2'. This example relates to a case where the recording is made on a track N. The recording data 101' is mark-edge recorded on a magneto-optical disk medium by the recording beam 2' through a recording current driving circuit 5'. The recorded data is read by the reproduction beam 20 and is outputted to a reproduction amplifier 3'. At the reproduction amplifier 3', the reproduced signal is amplified and is outputted to a clock extraction circuit 21 and a reproduced data detection circuit 22. At the clock extraction circuit 21, the clock extraction from the reproduced signal is carried out, and the reproduction clock 100' is outputted to the reproduced data detection circuit 22, a recording data delay circuit 6' and a data comparator circuit 7'. At the reproduced data detection circuit 22, the reproduced signal amplified by the reproduction amplifier 3' is converted to a binary signal, is latched by the reproduction clock 100' from the clock extraction circuit 21, and is outputted to the data comparator circuit 7'. The data comparator circuit 7' receives a delayed recording data 102', which has been timing-adjusted by the reproduction clock 100', from the recording data delay circuit 6', and an output 103' from the reproduced data detection circuit 22, compares these data, and outputs a verify error signal 104'. At a record judging circuit 8', when the verify error signal 104' is outputted from the data comparator circuit 7', it is judged whether the recorded state of the data signal recorded on the magneto-optical disk medium requires verification. Then, the record judging circuit 8' outputs a record judging signal 105' to the system side.
The deficiency in the above system is that the two-beam optical head has a problem in positioning the beams at the recording track, or that the need for the reproduction clock extraction inevitably requires a complex construction. Thus, the problem remains that the system requires a recording time of more than two times as compared with the magnetic disk device.
A prior art example in which it is attempted to reduce the time required in making verification during the recording in a magneto-optical disk so as to shorten the recording time, is disclosed in Japanese Patent Application Kokai Publication No. Hei 5-62273. In this example, the level of the reproduction signal ("RF signal" in the reference) from the optical head during the recording is detected by a level detection circuit. Here, the verification is made only when this reproduction signal level has become a level lower than a predetermined level. Since no verification is made when the level is above the predetermined level, that is, not all recorded data are verified, it is said that the recording time is shortened.
Another prior art example which does not relate to a magneto-optical disk medium but relates to a write once read many type optical disk is disclosed in Japanese Patent Application Kokai Publication No. Sho 57-212629. In this example, the verification is made by monitoring the quantity of reflected light during the recording.
The above method in which the quantity of reflected light is monitored is effective in determining whether to re-verify or whether to transfer a defective portion to a replacement sector, but there are still problems as explained below.
That is, since the verification depends on changes in the quantity of the reflected light, the change in the reflected light caused by contaminants such as grease or dirt adhering to the surface of the optical disk leads directly to the determination that there is a defect. However, as is apparent from the performance index defined approximately by the product of "the square root of the reflectivity from the optical disk medium" and "the Kerr rotation angle", it is known that the lowering of the reflectivity leads to an increase in the Kerr rotation angle. Here, the verification is made directly based on the change in the reflectivity as being the existence of defects, and this presents a problem in the verification reliability.
Further, in the conventional magneto-optical disk recording device in which the verification is made during the recording only by checking the quantity of the reflected light, there remains a possibility that the presence of a minute scratch on the magneto-optical disk medium or a stain on a surface of the medium that is not a problem in practice is erroneously recognized as being a problem. This makes the verification during the recording meaningless, thus affecting the efficiency of the operation for a reason such as necessitating a further precise verification to be carried out after more than one cycle of the disk rotation from the start of the data recording.
Also, in the conventional magneto-optical disk recording device where only the quantity of the reflected light is relied upon as explained above, it is impossible to make the checking of defective erasing so that there is a possibility that the recording is made at a defective portion, leading to a problem of the lowering of throughput of the device.
The prior art includes a proposal of a system wherein a magneto-optical reproduction signal is detected by a level detection circuit during the recording, which is disclosed in Japanese Patent Application Kokai Publication No. Hei 5-62273. This proposal relates to a method in which the detection is not made on a bit-by-bit basis but is made to detect a reproduction signal level (an envelope level in which a change with time is long) by a fixed threshold level. Thus, the detected signal cannot be regarded as representing an exact bit-by-bit recording state, and the detection is of low accuracy. With the method with which whether or not a reproduction signal level is above a predetermined level is judged, there is a problem that, where the recording power becomes large, it is possible for a bit involving a recording error to be incorrectly recognized as being normal. In the proposed example, since the fixed threshold level is used for the judgment, there is a problem that, when an envelope DC change caused by a birefringence inherent to the magneto-optical system has occurred, there is a possibility for the abnormal recording to be recognized as being normal.